not as aggressive as red terrors but it also depends on what you keep them with. My first Green terror I kept with a texas and I couldn't understand what the fuss was about. I had to move him because the Texas turned on him. I moved him in with severum and then I saw the aggression. I just bought two little 2" guys and 75 gallons wasn't enough territory for one of them so I had to get rid of it. The one I kept is pretty mellow. So long story short I have no idea I think it is a crap shoot with these guys lol. But I would say less aggressive than the other large cichlids.